The manufacture of therapeutically active proteins requires proper folding and processing prior to secretion. Proper folding is particularly relevant for proteins, such as antibodies, which consist of multiple subunits that must be properly assembled before secretion. Eukaryotic cells have adapted a system that ensures the proper folding of proteins and the removal of misfolded proteins from the secretory pathway. This system is called the unfolded protein response (UPR) pathway, and it is triggered by the accumulation of misfolded proteins in the endoplasmic reticulum (ER).
An early event of the UPR is the activation of the transcription factor Xbp1, which in turn activates the transcription of endoplasmic reticulum degradation-enhancing alpha-mannosidase-like protein 2 (EDEM2), a member of the endoplasmic reticulum associated degradation (ERAD) pathway. EDEM2 facilitates the removal of misfolded proteins. The ERAD pathway comprises five steps: (1) chaperone-mediated recognition of malformed proteins, (2) targeting of malformed proteins to the retrotranslocation machinery or E3-ligases, which involves EDEM2, (3) intitiation of retrotranslocation; (4) ubiquitylation and further retrotranslocation; and (5) proteosome targeting and degradation.
Antibodies are multi-subunit proteins comprising two heavy chains and two light chains, which must be properly folded and associated to form a functional heterotetramer. Any improvement in the efficient and accurate processing of the heavy and light chains to improve the yield or titer of functional antibody heterotetramers is desired.